1. Field of the Invention
The invention relates to a torque limiting roller and a medium separating mechanism using the same, and more particularly to a bidirectional torque limiting roller and a medium separating mechanism using the same.
2. Related Art
A torque limiting roller can provide limiting torque. When the driving torque of a driving roller for driving the torque limiting roller is greater than the limiting torque of the torque limiting roller, the torque limiting roller can be rotated by the driving roller. When the driving torque of the driving roller for driving the torque limiting roller is smaller than the limiting torque of the torque limiting roller, the torque limiting roller cannot be rotated.
FIG. 8 is an exploded illustration showing a conventional torque limiting roller 100. Referring to FIG. 8, the conventional torque limiting roller 100 includes a coupler 110, a roller 120 and a torsional spring 130. The torsional spring 130 is disposed between the coupler 110 and the roller 120, and one end of the torsional spring 130 is mounted on the coupler 110 or the roller 120. When the roller 120 is rotated, the inner diameter of the torsional spring 130 is decreased or increased in different rotation directions. The torsional spring 130 with the increased inner diameter is in frictional contact with a shaft surface 112 of the coupler 110 and a shaft surface 122 of the roller 120 so that the limiting torque is provided. The torsional spring 130 with the decreased inner diameter cannot provide the limiting torque. Thus, the conventional torque limiting roller only can provide the unidirectional limiting torque, but cannot provide the bidirectional limiting torque. In addition, the control of the contact surface is more sensitive. If the dimensions have errors, the provided limiting torque is not perfect. Thus, the torsional spring 130 has to be made with precision, and the cost will be higher.
Thus, it is an important object of the invention to provide a low-cost torque limiting roller capable of providing the bidirectional limiting torque.